This invention relates to memories which are partially good, and more particularly to memories which use an array division technique for providing a memory which is partially good.
Memories, having a fabricated number of memory elements, are sometimes sold as having only half of the fabricated number of memory elements being good. The purpose for doing so is to get some value from a part that would otherwise be unmarketable. A technique for array division disclosed in U.S. patent application No. 305,830, Memory with Permanent Array Division Capability, Kuo, overcomes requiring a response from the user, such as, applying either a positive or a negative power supply voltage to an address pin. This was achieved by programming an address buffer to apply a particular address signal at only one logic level so that only a memory cell in the half of the array corresponding to that logic level could be selected.
For a memory with four quadrants, a logic high could correspond to a first and a second quadrant, and a logic low could correspond to a third and a fourth quadrant. In such a case a half good memory can be obtained only if both the first and second quadrants are good or both the third and fourth quadrants are good. Other combinations of two good quadrants, e.g., first and third, first and fourth, second and third, and second and fourth, could not be utilized to obtain a half good memory, however.